Field of the Invention
The present invention relates to image stabilization technology for compensating image blurring (for preventing image degradation) due to shake of an apparatus such as camera shake.
Description of the Related Art
Cameras provided with an image stabilization apparatus (consisting of an image stabilization unit, a driver, a shake detection unit, etc.) that prevents image blurring due to camera shake or the like are currently available, and factors inducing the photographer to make a photographic error have mostly been eliminated.
Here, an image stabilization apparatus that prevents image blurring will be briefly described. Camera shake due to the photographer is usually vibration having a frequency of 1 Hz to 10 Hz.
In order to enable photographs without image blurring to be taken even when camera shake occurs, vibration of the camera due to camera shake has to be detected and a lens for image blurring compensation (hereinafter, compensation lens) has to be displaced according to the detected value.
However, with photography at close range (photography at high magnification), image degradation due to so-called parallel shake that occurs in a direction parallel to or perpendicular to the optical axis of the camera and is undetectable with only a gyroscope also cannot be disregarded. Parallel shake needs to be actively detected and compensated under conditions where, for example, images are captured within 20 cm or so of the subject such as with macro photography, or the focal length of the photographic optical system is extremely long (e.g., 400 mm) despite the subject being positioned at a distance of one meter or so.
With technology disclosed in Japanese Patent Laid-Open No. 7-225405, there is a problem in that the output of the accelerometer tends to be affected by disturbance noise and changes in the environment such as temperature change, and these destabilizing factors are further magnified by performing second order integration, making it difficult to compensate parallel shake with high accuracy.
In Japanese Patent Laid-Open No. 2010-25962, destabilizing factors of the accelerometer such as the above can be mitigated by only deriving the rotation center for frequency bands that tend not to be affected by disturbance. In Japanese Patent Laid-Open No. 2010-25961, technology is disclosed for calculating compensation values up until the time when the image capture operation on the image stabilization target is started, and performing parallel shake compensation during image capture using the compensation values.
However, with a method of performing parallel shake compensation using the rotation radius of angular shake, the rotation radius needs to be correctly derived, and the following issue arises.
That is, although the detection accuracy of the various sensors is important in the case of using an accelerometer and a gyroscope to compute the rotation radius, computation of the rotation radius is not correctly derived in the case where sensor noise exerts a significant influence, and a suitable parallel shake compensation effect is not obtained. Particularly in the case where the proportion of noise amount in the accelerometer output is large, there is concern that the rotation radius will be misestimated, resulting in a large amount of parallel shake compensation, and deterioration in image stabilization performance due to overcompensation.
Because the amount of noise is generally constant regardless of the magnitude of acceleration, in the case where there is significant parallel shake, that is, in the case of a high acceleration output value, the noise exerts little influence on the rotation radius estimation, and the amount of parallel shake compensation can be correctly derived.
However, in the case where there is very little parallel shake, that is, in the case where an acceleration output value is small, the noise exerts a significant influence on the rotation radius estimation, making it difficult to correctly derive the parallel shake compensation amount. In other words, differences in the amount of camera shake due to the shooting posture or the like will give rise to differences in the detection accuracy of parallel shake, that is, differences in the image stabilization effect.
Also, when using a gyroscope and an accelerometer to compute the rotation radius, the following problems arise when attempting to derive the rotation radius and perform parallel shake compensation in the case where the correlation between the angular velocity signal and the acceleration signal is low. That is, because parallel shake is misdetected since the correlation between the output of the gyroscope and the output of the accelerometer is low, image stabilization performance may be adversely affected.
Furthermore, the correlation relationship may differ greatly depending on the orientation of the camera. For example, since roll angular velocity cannot be detected in the case where a pitch and yaw dual-axis gyroscope is provided, when the roll rotation exerts a significant influence, not only is it impossible to perform suitable parallel shake compensation but controllability deteriorates due to overcompensation.
Also, the drive axis that tends to be affected by roll compensation changes depending on the inclination status (shooting orientation) of the camera (e.g., parallel shake due to the influence of the roll angular velocity tends to occur on the yaw axis in the case of a normal status and on the pitch axis in the case of a vertical status).